Marine related bulkheads constructed along the coast of Alaska experience some of the most severe environmental conditions known, including high waves and wave scour, earthquakes, ice, high tide variations, high phreatic water levels, weak soils, exposed or near-surface bedrock, heavy live loads, and difficult construction conditions. The need for low-cost, high load capacity docks and structures that allow field adaptation to changing field conditions has resulted in a development of various sheet pile retaining structures.
Flat steel sheet piles have been used in simple structures featuring primarily tension or membrane action. Foundation designs of cellular cofferdams are discussed in detail in the text by Joseph E. Bowles, Foundation Analysis and Design (1977) herein incorporated in its entirety by reference. One configuration, a closed cell flat sheet pile structure, had been successfully used for many years for a wide variety of structures including cofferdams and docks. The most common use for flat sheet piles has been in closed cellular bulkhead structures of various geometrical arrangements. Another configuration includes a diaphragm closed cell structure. By closing the cell structure, the entire structure acts as a deadman anchor in the retaining system to provide additional retaining support. However, positive structural aspects of these closed cell structures are often offset by high construction costs. Several factors have contributed to higher costs, including, for example: multiple templates required for construction alignment; close tolerances; difficulty with driving through obstacles and holding tolerance; backfilling operations using buckets or conveyors; and difficulty compacting the backfill.
Another sheet pile retaining form has been the tied back wall masterpile system with flat sheet piles acting as a curved tension face. Tieback anchors with deadmen are connected to the curved tension face to provide lateral retaining strength. This configuration allows a higher load to be retained with fewer sheet piles used as the anchors and the sheets work in concert to retain the earth load. However, tied back sheet pile walls often require deep toe embedment for lateral strength, and if that toe embedment is removed for any number of reasons, wall failure will result. This configuration further requires excavation for placement of the soil anchors, or an expensive and time consuming drilling operation to install the soil anchors, at the appropriate depth to integrate them with the sheet pile wall. Additionally, tied back walls are at risk in environments where waves overtop the wall and result in scour. Scour undermines the base of the bulkhead and the needed toe support resulting in failure of the bulkhead. The tied back walls are subject to failure during seismic events at the tied back connection to the wall and failure due to corrosion either at the tied back connection to the wall or the wall itself where corrosion of the exposed wall at the air/water interface occurs.